The term testlets was first officially introduced in late 1980s and defined as
“
a group of items related to a single content area that is developed as a unit and contains a fixed number of predetermined paths that an examinee may follow.”
1)
Simplified, testlets:2)
are small tests of single units from which together construct a test;
should be small enough to manipulate but big enough to carry their own context;
can be used to balance contents of a test.